I. Field
The present invention relates generally to communication, and more specifically to techniques for selecting rates for data transmission in a multiple-input multiple-output (MIMO) communication system.
II. Background
A MIMO system employs multiple (T) transmit antennas at a transmitting station and multiple (R) receive antennas at a receiving station for data transmission. A MIMO channel formed by the T transmit antennas and the R receive antennas may be decomposed into S spatial channels, where S≦min {T, R}. The S spatial channels may be used to transmit data in parallel to achieve higher throughput and/or redundantly to achieve greater reliability.
Each spatial channel may experience various deleterious channel conditions such as, e.g., fading, multipath, and interference effects. The S spatial channels may experience different channel conditions and may achieve different signal-to-noise-and-interference ratios (SNRs). The SNR of each spatial channel determines its transmission capacity, which is typically quantified by a particular data rate that may be reliably transmitted on the spatial channel.
Rate selection refers to the process of selecting suitable rates for data transmission, e.g., on the spatial channels of the MIMO channel. A “rate” may be associated with a particular data rate or information bit rate, a particular coding scheme or code rate, a particular modulation scheme, and so on to use for a data stream. For a time variant MIMO channel, the channel conditions change over time and the SNR of each spatial channel also changes over time. The different SNRs for different spatial channels plus the time varying nature of the SNR for each spatial channel make it challenging to select the proper rates for the spatial channels.
There is therefore a need in the art for techniques to select rates in a MIMO system.